1. Field of the Invention
The present invention generally relates to circuit boards used for information processing devices such as electronic computers. More particularly, the present invention is concerned with a circuit board having a normal operation mode and a backup operation mode, and an information processing device having such a circuit board.
Information processing devices such as electronic computers are supplied with power as long as the devices are working. When the power supply is completely stopped, the computers do not work at all. However, some computers are required to save information stored in memories of the computers even when the power supply is OFF. For example, there are computers which are not required to process jobs in the night, holidays or the like, but are required to save information stored in the memories. Such computers are employed by bankers or the like. In such cases, the memories are supplied with power in a backup mode (which is also called a hot-standby state), in which the power is generated by a backup power supply unit, such as a battery. This is also the case when a power failure or a power cut takes place.
Generally, a maintenance operation is carried out in the normal operation mode or the completely disabled state. However, recently, it has been desired that the maintenance operation be carried out in the backup operation mode. For example, when a fault has occurred in a circuit board such as a printed circuit board on which memory chips (loads) are mounted, the faulty circuit board maintained in the backup mode is replaced by a new one while the other circuit boards are kept activated in the backup mode. In the maintenance operation, it is necessary for the computer system set in the backup mode to be affected by the replacement operation.
2. Description of the Prior Art
FIG. 1 is a block diagram of a part of a conventional computer, which has a plurality of memory boards including memory boards 1-1, 1-2, 1-3, on which memory chips (ICs) are mounted. The memory boards 1-1-1-3 are connected to a power supply line to which a normal operation power supply line 4 is coupled via a diode 2 and a backup power supply line 5 is coupled via a diode 3. A power supply unit for the normal operation (not shown) is connected to the line 4, and backup power supply unit for the backup operation (not shown) is connected to the line 5. Of course, other lines such as address bus lines and data bus lines are provided on the circuit boards and are connected to a main body or host device (not shown) of the computer via connectors and bus lines.
The memory boards 1-1 through 1-3 can be operated in either the normal operation mode or the backup operation mode. In the normal operation mode, the memory boards 1-1 through 1-3 are supplied with a dc power supply voltage via the normal operation power supply line 4, the diode 2 and the power supply line 6. In the example shown in FIG. 1, the power supply voltage is 3.3 V. In the backup operation mode, the memory boards 1-1 through 1-3 are supplied with a dc backup power supply voltage via the backup operation power supply line 5, the diode 3 and the power supply line 6. In the example shown in FIG. 1, the backup power supply voltage is also 3.3 V. In FIG. 1, the backup power supply voltage 3.3 V is illustrated as VB.
Each of the memory boards 1-1 through 1-3 is equipped with a mode setting function controlled by an upper device or a main body (frame) or a host device of the computer. For example, the mode setting function is implemented by an electronic mode setting switch, which is controlled by a control signal from the main body of the computer. When the memory boards 1-1 through 1-3 are set to the backup mode by turning OFF the corresponding mode setting switches, only some memory chips in each of the memory boards 1-1 through 1-3 are connected to the power supply line 6. In the backup operation mode, the backup operation power supply unit is connected to the line 5, while the normal operation power supply unit is disconnected from the line 4. In this state, the memory boards 1-1 through 1-3 are operated in the backup mode in which some memory chips are not supplied with power. For example, each of the memory boards 1-1 through 1-3 consumes power equal to, for example, one tenth of the power consumed in the normal operation mode.
When the computer is switched from the backup operation mode to the normal operation mode, the normal power supply unit is connected to the line 4, and the backup operation power supply unit is disconnected from the line 5. Further, the computer main body turns ON the mode setting switches of the memory boards 1-1 through 1-3.
As described before, it is desired that the maintenance operation be carried out without completely turning OFF the whole computer. In other words, it is desired to save information stored in the memories even when the computer main body does not process the jobs at all. If a fault has occurred in the memory board 1-1, this faulty memory board 1-1 is replaced by a new one or repaired one in the backup operation mode. It will be noted that the other memory boards are kept active in the backup operation mode and information stored therein is saved.
When the faulty memory board 1-1 is detached from the computer in the backup operation mode, the supply of electricity to the mode setting switch of the board 1-1 is stopped and the mode setting switch is switched to the original state, so that all the memory chips on the board 1-1 are set in the normal operation mode. That is, all the memory chips on the board 1-1 will be supplied with power if the board 1-1 is connected to the line 6 again after it is repaired. The same situation as described above takes place when a new memory board is connected to the line 6. The built-in switch is in the original state (normal operation mode), and thus all the memory chips on the new memory board is supplied with power.
When the repaired memory board or the new memory board is connected to the line 6 in the state in which the computer is in the backup operation mode, the above board operates in the normal operation mode until it is set to the backup operation mode, and hence consumes power as much as the board consumes in the normal operation mode. The power supply unit used in the backup operation mode is a battery. Hence, the sufficient driving ability of the battery will be lost soon after the repaired memory mode or the new one is connected to the line 6. Hence, it is inhibited from performing the repair or replacement operation on the memory boards in the backup operation mode.